You're going to be bringing in an Air 3S which you purchased in a foreign country but want to use on your visit in the US?
Shouldn't be a problem. You have nothing to declare, though if you still have it sealed in the box, customs agents might suspect you plan to sell it to someone in the US.
You don't go through customs when leaving the US.
It's more of an issue for Americans who purchase products of any kind, not just drones, in foreign country and bringing them back, not declaring it, to avoid duties or tariffs which would be paid by importers bringing the products into the US to resell here.